Mendel's 1st Law: Topics for Class Summary

Keywords

What determines the dominance of one allele over another?
How are alleles separated and distributed in gamete formation?
What is the difference between phenotype and genotype?
How are genotypic and phenotypic proportions represented in the F1 and F2 generations?
What are the possible allele combinations in the offspring resulting from heterozygous parents?

Understanding the concept of allele pairs: one inherited from the mother and one from the father.
Understanding the segregation of alleles during meiosis and their distribution in gamete formation.
Identifying genetic inheritance patterns according to Mendel's first law.

Alleles: Variants of a gene that occupy the same position on homologous chromosomes.
Dominant: Allele that expresses its phenotype even in the presence of another different allele.
Recessive: Allele whose phenotype is masked in the presence of a dominant allele.
Homozygous: Organism that has two identical alleles for a specific gene.
Heterozygous: Organism that has two different alleles for a specific gene.
Phenotype: Observable characteristics of the organism.
Genotype: Genetic constitution of the organism; the combination of alleles.

Not specifically applicable to Mendel's 1st Law, but understanding probability is essential to predict phenotype and genotype proportions.

Genes: Basic units of heredity, found at specific loci on chromosomes. Responsible for controlling and transmitting hereditary traits.
Chromosomes: Structures formed by DNA and proteins, containing many genes. Humans have 23 pairs of chromosomes in each somatic cell.
Alleles: Alternative forms of the same gene that occupy the same position (locus) on homologous chromosomes. Each individual inherits one allele from each parent.
Dominant: Allele that expresses its effect independently of the other allele present in the pair. Represented by an uppercase letter (e.g., 'A').
Recessive: Allele whose effect is masked in the presence of a dominant allele. Represented by a lowercase letter (e.g., 'a').
Homozygous: Also known as pure, is the individual that has both alleles the same for a specific gene (AA or aa).
Heterozygous: Also known as hybrid, is the individual that has different alleles for a specific gene (Aa).
Phenotype: The observable physical characteristics of the individual, resulting from the interaction of the genotype with the environment.
Genotype: The genetic composition of the individual, which determines its developmental potential.

Allele segregation is a fundamental process where, during gamete formation (meiosis), alleles for a gene separate so that each gamete carries only one allele for each locus.
The phenotype is the physical manifestation of a genetic trait, such as eye color, while the genotype is the set of genes that determine this trait.
Mendel's 1st Law, or Law of Segregation, states that each trait is determined by pairs of alleles that separate during gamete formation, ensuring that each gamete has only one allele from each pair.
Understanding homozygotes and heterozygotes is crucial for predicting phenotypic and genotypic proportions in offspring.

P Generation: The parents in Mendelian experimentation, each contributing one allele to the offspring.
F1 Generation: The first filial generation, where all are heterozygous if the parents are homozygous for different alleles.
F2 Generation: The second filial generation, obtained by crossing F1 individuals, where phenotypic and genotypic proportions can be predicted using a Punnett square.

Example of pea flower color: Mendel observed that by crossing a purple flower plant (P) with a white flower plant (p), all F1 generation had purple flowers. This showed that the allele for purple color was dominant over the allele for white color.
- By self-fertilizing the F1 plants, he obtained an F2 generation with a phenotypic ratio of 3:1, with three plants having purple flowers for each one with white flowers, demonstrating allele segregation and recombination.
Probability Calculation:
- When crossing two heterozygous individuals (Aa x Aa), the probability of obtaining a descendant with a dominant phenotype (A-) is 75% (3 in 4), while the probability of obtaining the recessive phenotype (aa) is 25% (1 in 4).

Law of Segregation: Proposes that each individual has a pair of alleles for each gene, which separate during gamete formation. Each gamete receives only one allele from each pair.
Dominant and Recessive Alleles: The dominant phenotype is expressed even in the presence of a recessive allele. The recessive phenotype is manifested only in recessive homozygotes.
Determination of Phenotypes and Genotypes: Emphasizes the ability to predict an organism's characteristics based on the parents' genotypes.
Predictive Crossbreeding: Uses the Punnett square tool to calculate the probabilities of genotypes and phenotypes in offspring.

Organisms inherit two alleles for each gene, one from each parent, which determine the phenotype.
The manifestation of a trait depends on the interaction between dominant and recessive alleles.
The expected genotypic ratio in offspring of heterozygous parents is 1 AA: 2 Aa: 1 aa.
The resulting phenotypic ratio often follows the 3:1 relationship, with three individuals exhibiting the dominant trait for each one showing the recessive trait.
Understanding Mendel's 1st Law is essential for genetic analyses, inheritance studies, and interpretation of genetic patterns in crosses.